Increased skeletal fragility is a major concern in the health care of the elderly. Bone primarily consists of a hard mineral phase and a compliant collagenous matrix. It has been speculated hitherto that the mineral phase imparts the stiffness to bone, while the collagenous matrix enhances the toughness of the tissue. The long-term goal of this study is to elucidate the role of collagen in determining bone mechanical integrity and its contribution to age and disease-related increases in bone fragility. In this study, it is hypothesized that age-related increase of bone fragility is attributable to the adverse changes in molecular and structural properties of collagen in bone. To test this hypothesis, four specific aims will be addressed. Specific Aim 1 is to develop a novel methodology for quantification of collagen denaturation in the non-calcified and calcified collagen portions in bone. Using this technique, it is expected to be able to detect the difference in collagen denaturation in both the non-calcified and calcified collagen portions between specimens. Specific Aim 2 is to determine the correlation of the collagen denaturation in bone with bone remodeling. The technique developed in Aim 1 will be used to determine collagen denaturation in bone, while bone remodeling will be assessed by examining the volume fraction of osteoids (non-calcified collagen matrix) and the number and volume fraction of secondary osteons in bone. Specific Aim 3 is to determine the age-related changes in collagen denaturation in both non-calcified and calcified collagen portions in bone, and to explore the correlation of such changes with the biomechanical integrity of the collagen network and bone. Finally, Specific Aim 4 is to examine changes in collagen crosslinks concentrations in bone as a function of age and to explore their correlation with the age-related deterioration in bone biomechanical integrity. In this study, mechanical testing will be performed to determine the elastic modulus, strength, and fracture toughness of the demineralized bone and bone samples. A selective digestion technique will be employed to quantify the amount of normal and denatured collagen molecules. The collagen crosslinks concentration will be determined using a simplified HPLC technique. This study will, for the first time, provide an insight into the structure-function relationship of bone and its correlation with age-related deterioration in the biomechanical integrity of bone. Also, the techniques developed in this study will facilitate future studies on the collagen network as determinants of bone quality.